A damper pulley assembly normally comprises a hub connected rigidly to an internal combustion engine crankshaft; a pulley connected to the hub; and a seismic mass connected to the hub to define a dynamic torsional vibration damper.
More specifically, the pulley is connected, to rotate with respect to the hub, by an elastic member interposed between the pulley and the hub. The most commonly used elastic members are a ring of elastomeric material, or one or more metal spiral or helical springs.
Because of the increase in power absorption by the accessory devices driven by the accessory drive, the pulley is now subjected to severer stress than in the past.
When power absorption exceeds a given threshold, an elastomeric ring cannot guarantee transmission of the necessary torque, and is therefore replaced with a metal spring.
A metal spring has better heat resistance and, in particular, can be used at higher operating temperatures than an elastomeric ring.
Moreover, failure of the elastic member of a damper pulley assembly may arrest operation of the accessory drive and so endanger passengers and result in serious damage to the vehicle.